How to plant a tree.
Including the Dryland Planting Technique used in southern Australia.
First a few don’ts……
Digging a large, deep hole and throwing a handful of fertilizer in the bottom is not the best way to plant a tree.
This just creates a sump of cultivated open pore space soil, compared to the surrounding soil, that allows for too much water to collect in the rainy season and resulting root rot, and too much drainage during the dry season.
Small amounts of fertilizer are better off on the surface; it can then enter the soil slowly as it dissolves into solution.
It is also seldom wise to add to the hole, manures, organic matter or ‘good friable soil’ from another source. Again, these create a sump of open material and the decomposing plant material may introduce fungi and bacteria harmful to the tree.
Do not add gravel, broken bricks, rocks or other course drainage material to the base of the hole, unless this drainage area is connected to a pipe that will convey the water away. These coarse materials also create a sump that will be seasonally too wet and too dry.
How to plant a tree:
1. Water the tree well in its container before planting.
2. Dig a hole the same depth as the root ball or plant container.
3. The hole can be wider than the root ball by 2 to 3 times but this is not essential. Loosening this side of hole soil will encourage lateral ‘feeder’ root growth.
4. Test the soil’s drainage — after digging the hole fill it with water and observe how quickly the water drains away. If the water is still present after 24 hours, don’t plant the tree. See below.
5. Remove the plant from its container by placing your hand over the top of the root ball with the fingers either side of the stem, turn the plant upside down, using your other hand to hold the container, then tap the edge of the container on a raised solid surface (eg a spade upright in the ground or the edge of a wheelbarrow, when planting small plants I’ve used the toe of my steel capped boot to tap the pot against) and the container should slide off. Then inspect the roots ensuring they are not ‘pot bound’ ie not growing around and around the root ball, if so, gently tease out some of the roots, this is in order to stop the roots continuing to spiral around once planted.
6. Place the plant in the hole, ensuring the top of the root ball is at ground level, then backfill the hole with the same soil you dug out, push the soil down firmly making sure there are no large air pockets left unfilled. It is most important that no part of the root ball potting media is left exposed at or above the surrounding soil surface. The open pore spaces of the potting media may act as a wick, whereby moisture can move up by capillary action to the air and dry out the root ball.
7. Water thoroughly to ensure the backfilled soil and root ball are saturated, this will also help fill any large air spaces with soil. A little additional backfill soil maybe needed at this stage if any large air spaces collapse.
8. Mulch around the plant to protect the soil from sunlight heat and the impact of rain, a layer 50–100mm should be sufficient, too thick a layer may stop rainwater penetrating into the soil. Keep the mulch about 50mm away from the tree stem to avoid damp conditions causing collar rot.
9. Staking if required, can be done after planting if the stake is kept far enough away from the stem to ensure the stake doesn’t damage the root ball. This distance provides for loose tying which ensures the stem can still move about in the wind, allowing strength to gradually build up in the woody tissues of the stem.
Timing of planting.
If your plant is in a pot or container of potting media and you are able to water the plant through the first dry summer, then you can plant any time of the year. Having said that the milder seasons of Spring and Autumn are preferable planting seasons as they are less stressful on the young plant.
Deciduous open rooted trees are planted in winter when they are deciduous. Remove the material they are wrapped in; generally, saw dust or wood shavings, used to keep the roots moist in transport.
Citrus are planted in the warmer months, late spring and summer. They are sub-tropical plants, originally from Southeast Asia and will be set back by root rot if they are planted into cold soil. Good drainage is also most important for citrus.
Soil can be improved long before planting with the placing of animal manure and organic matter as a mulch on the soil surface, and doing this the year before planting is best.
Soil microorganisms, bacteria and fungi, can then start to breakdown the organic matter and slowly introduce it to the soil. Nature’s cultivators, the earthworms, will be encouraged and by their burrowing increase the soil aeration and drainage even into the subsoil.
Drainage was mentioned before and the drainage of the soil and subsoil when planting is one of the first considerations, after suitable species selection.
Subsoil is used by tree roots to gain stability, it is a more constant source of soil moisture and deep roots are able to absorb nutrients leached into the subsoil, bring them up into the plant. From the plant, nutrients will eventually be deposited on the surface in dead leaves as mulch and are decomposed by bacteria and thus will continue the cycle back into the soil and subsoil.
Topsoil is the most fertile layer containing more nutrients and many differing particles of organic matter and humus. Humus is generally thought of as the final stage of organic matter after decomposition. It is the soil layer of most activity by micro and macro-organisms. It should have good aeration, water infiltration and drainage.
As stated, if the soil doesn’t drain, don’t plant. Little or no drainage indicates that there is an impervious layer below the surface. This is likely to be a subsoil layer of compacted clay and if that is the case a deeper hole to break through the layer is needed. This can be back filled with the same subsoil and compacted before planting.
Alternatively, the soil maybe be sandy with a layer of limestone rock just below the surface, this is often indicated by the inability to dig any planting hole at all. Some mechanical aid might be needed, eg a tractor with a ripper, to break through this rock layer to enable tree roots to penetrate.
If your planting site soil has been compacted by human activities such as foot or hoof traffic or from vehicle passage, mechanical assistance will be needed to aerate the soil, either by hand digging or ploughing.
A dryland planting technique has been widely used for revegetation in southern Australia to reinstate the original vegetation that has been cleared.
Its main principles are:
Use of local indigenous species.
Plants grown in tubes ie small seedling size at planting.
Planting during the wet winter.
Weed control before planting.
Protection from grazing animals.
Locally occurring species are selected as these are adapted to the local conditions and have a greater chance of success and of re-establishing the ecosystem. The plant species can be determined by investigating species in remnant vegetation from before European settlement. Patches of original vegetation may still remain on roadsides, in cemeteries or in reserves.
As many species as possible should be represented in the revegetation species mix. Local provenance seed, from species adapted to local conditions, should be used as these will perform better. Numbers of each species can again be judged by observing the different species density and spacing. As a rule of thumb, there will be far more grass and shrub type plants than trees.
Plants are often grown in small tube containers, eg. 50 x 50mm square and 150mm high. The plant being small reduces transplant shock as the root system is also still small, and the seedling is planted before it grows its deep roots to access soil moisture lower down in the soil profile.
Planting is into small holes, just large enough to hold the dimensions of the root ball from inside of the tube, ensuring that the top of the root ball is at or just below the soil surface. Planting tools such as the Pottiputki (in sandy soils) and the Hamilton Tree Planter make the planting of large numbers easier but a long handle spade is still most useful.
Planting can start after the opening rains which have often been in April (mid-autumn) but does seem to be getting later. Early wet winter season planting allows for root growth while the soil is moist. In higher rainfall areas, planting can be later in the winter and indeed a spring planting is often needed in frost prone areas.
Watering the plants in their containers just before planting is most important to ensuring greater survival in this dryland planting technique where follow up watering isn’t possible.
Submerging the whole tray of seedling tubes, just for 20 seconds, in a large tray of water near the planting site, will ensure the tubes are saturated with water at planting. Once planted into moist soil this should provide the plant with enough soil moisture for a month without rain. Another technique, if enough water can be brought to the planting site, is to plant the previously saturated tubes into holes filled with water, again to provide as much soil moisture as possible. If follow up watering is possible over the dry summer months this will improve survival rates, vehicle or trailer mounted farm fire-fighting units have proved useful for this.
Fertilizer and introduced mulch are not used with this planting technique. Both will introduce nutrients that will encourage weed growth. The local indigenous species used are adapted to the naturally infertile soils. Keep in mind that if the planting site has been previously used for cropping or pasture it will probably have been fertilized with Superphosphate fertilizer which will encourage weed growth.
Weed control is generally necessary to reduce competition for soil moisture and for sunlight. It is important to control perennial weeds in particular as the revegetated species will struggle to compete with weeds such as Kikuyu, couch and buffalo grass and woody weeds such as blackberries and gorse.
Follow up weed control for the first few years may be necessary to reduce competition for resources, to reduce fuel load for fire hazard and to improve the aesthetics of the site.
Seedling guarding of individual plants with a plastic guard will protect the seedling from frost but is also of great importance to protect the seedling from grazing by Rabbits, Hares and Kangaroos. Kangaroos are able to graze the revegetation seedlings once they grow to the top of the tree guard but often seedlings will then outgrow the grazing the following year. Hares will nibble the base of the seedling stem, such that the stem falls over on the ground. The Hares are thought to be sharpening their teeth on the stem, as they don’t eat any of the foliage. I’ve heard them called environmental vandals as they kill the plant without even getting any benefit of eating it.
Farm animal camp sites, for example sheep often camp in the highest corner of a paddock as it is generally warmer, have high concentrations of urine and faeces, causing high levels of nutrients and salts often making these sites difficult to establish plants. Such sites are best fenced off and left for a year or two while the weeds and rainfall gradually lower the nutrient levels.